In operations of a personal computer, a PDA, a portable terminal, and the like, input techniques done directly by a fingertip, a touch pen, or the like on a screen are conventionally known (for example, refer to Japanese Patent Application Publication No. 10-171600).
Such conventional techniques employ a method in which a piezoelectric or optical touch panel recognizes a coordinate at which a touch pen is manipulated and the control is informed to a control unit.
However, in the conventional touch panel technologies, parts and materials used are costly, and most of such parts and materials are produced integrally with hardware. Therefore, devices, such as a personal computer and an ATM, equipped with touch panels become very expensive.
To solve such a problem, in some cases, touch panels for being detachably mounted on display units have been developed (for example, refer to Japanese Patent Application Publication No. 2001-92595).    [Patent Document 1] Japanese Patent Application Publication No. 10-171600    [Patent Document 2] Japanese Patent Application Publication No. 2001-92595